1. Field of the Invention
The present invention relates to decorative laminates having an abrasion-resistant character which can be manufactured without scratching the caul plates and, more particularly, to overlays and multiple layer decor sheets with low scratch and abrasion resistant characteristics.
2. Description of Prior Art
High-pressure decorative laminates are laminated articles comprising plural layers of synthetic resin impregnated paper sheets consolidated or bonded together into a unitary structure under high heat and pressure. Conventionally, the decorative or print layer is a sheet of high quality cellulose fiber and fillers impregnated with a thermosetting condensation resin such as melamine formaldehyde resins. The decorative sheet may be overlaid with a low basis weight transparent sheet, which is also a sheet of cellulose impregnated with melamine formaldehyde resin. These sheets are bonded to a plurality of core or body sheets of a fibrous cellulosic material, usually unbleached Kraft paper, impregnated with a thermosetting phenol-formaldehyde resin. Typically, seven or eight core sheets are consolidated with only a single decorative sheet and a single overlay sheet to form a decorative laminate.
Decorative laminates are useful as surfacing materials in products ranging from table and counter tops to floors. In applications such as these, decorative laminates are imparted with functional properties to protect the decorative sheet from abrasive wear and tear, heat, moisture, chemicals and the like.
It is well known in the prior art that abrasion-resistance can be increased by incorporating mineral particles into the decorative layer, or by covering the decorative layer with a transparent overlay layer that incorporates such mineral particles.
U.S. Pat. No. 4,505,974 discloses a mar-resistant decorative laminate with an outermost layer containing mineral particles ranging in size from 0.005 to 0.1 microns. The minerals are silica and/or alumina and are positioned in the outermost 25 microns of the overlay.
Canadian Pat. No. 987,217 discloses a print receptive decor paper comprising print receptive fibers and abrasion resisting mineral particles, such as silica and/or alumina, having a hardness of 7-10 on the Mohs scale and an average particle size ranging from 10-75 microns.
Canadian Pat. No. 990,632 discloses an abrasive-resistant overlay sheet having embedded in its top surface particles, such as silica and/or alumina, having a size of 10 microns or greater in diameter, and having a Mohs' hardness of at least 8.0.
U.S. Pat. No. Re. 30,233 discloses a multi-layer decor sheet having abrasion-resisting mineral particles incorporated in the surface layer thereof. The multiple-layer decor paper is made up of a base layer of fibers and opacifying fillers, and a surface layer comprising fibers and abrasion resistant mineral particles. This sheet additionally may include an intermediate layer containing decorative inclusions. The surface layer is resin impregnated and thus no overlay is required, although one may be provided. The mineral particles disclosed have a hardness of 7 or more on the Moh hardness scale.
The overlays and multilayer decor papers of the prior art have been made with abrasion resistant materials such as silica, alumina, silicates, glass fibers, asbestos and the like which have been incorporated into the overlays and decor papers by various procedures. Overlays and decor papers made from such materials, however, have not been generally satisfactory for a number of reasons. Previous abrasion-resistant decor paper layers and overlays typically contain 1-30% by weight of a high hardness alumina in the 10-100 micron particle size range. Alumina particles less than 10 microns do not provide sufficient abrasion resistance to pass the NEMA standard for abrasion-resistant laminates. The particles with high hardness and larger particle size cause unacceptable caul plate scratching. This has necessitated refinishing the caul plates after 1-10 laminating cycles.
The purpose of this invention is to provide an overlay and multiple layer decor paper layer that reduces caul plate scratching while providing satisfactory abrasion resistance.